This invention relates to an insulation piercing terminal which is so designed that, when a covered wire is pushed in an insulation piercing slot, the conductor (core) of the wire is brought into contact with the insulation piercing terminal without removal of the insulating cover of the wire.
FIGS. 3(a) to 3(c) show a conventional insulation piercing terminal disclosed by U.S. Pat. No. 4,385,794. More specifically, FIG. 3(a) is a perspective view of the insulation piercing terminal, FIG. 3(b) is a sectional view taken along line IIIb--IIIb, and FIG. 3(c) is a perspective view showing part of a covered wire connected to the insulation piercing terminal.
In the figures, an insulation piercing terminal 1 is formed by blanking and press working a piece of thin metal sheet. Its front end portion is an electrical contact section 2 which is engaged with a mating terminal, and its rear end portion is a wire clamping section 3, and the middle portion between those front and rear end portions is an insulation piercing conductive portion 4. The electrical contact portion 2 is engaged with the mating terminal so that the former is electrically connected with the latter; the wire clamping section 3 has right and left retaining pieces (parts of the walls) 3a, which are bent inwardly to fixedly hold the wire W from above the insulating cover Wb; and the insulation piercing conductive section 4 is electrically connected to the conductor Wa of the wire W. The wire clamping section 3 is coupled through a first neck 6 to the insulation piercing conductive section 4, and the insulation piercing conductive section 4 is coupled through a second neck 7 to the electrical contact section 2.
The insulation piercing conductive section 4 has a front insulation piercing piece 10A and a rear insulation piercing piece 10B respectively at the front end and at the rear end. Each of the front and rear insulation piercing pieces 10A and 10B has a pair of right and left insulation piercing blades which are confronted with each other, forming an insulation piercing slot 12 in which the conductor of the wire is pushed. The wire clamping section 3, the insulation piercing conductive section 4, and the electrical contact section 2 have a bottom wall 7 formed of a belt-shaped common flat plate.
The insulation piercing conductive section 4 is U-shaped in section, having a part of the bottom wall 7, and a pair of right and left side walls 9 which are formed by bending the right and left edge portions of the bottom wall 7 upwardly. In this case, the right and left edge portions of the bottom wall are bent 90.degree. upwardly so that the resultant right and left side walls are confronted with each other, and suitable recesses 18 are formed on the bending lines by pressing, thereby to increase the rigidity of the portions corresponding to the bending lines. The insulation piercing blades 11 of the insulation piercing pieces 10A and 10B are formed by inwardly bending the front and rear edge portion of the side walls 9.
The wire W is connected to the insulation piercing terminal 1 as follows; One end portion of the wire W is laid on the rear end portion of the insulation piercing terminal 1 in such a manner that the one end portion of the wire W is in parallel with the rear end portion of the insulation piercing terminal 1. Under this condition, the one end portion of the wire W is pushed in the insulation piercing slots 12 of the insulation piercing conductive section 4 from above. In this case, the right and left insulation piercing blades 11 cut the insulating cover Wb of the wire W and contact the conductor Wa of the wire W. When the one end portion of the wire W is further pushed in, the conductor Wa is caused to go in between the right and left insulation piercing blades 11, thus being positively held by the insulation piercing blades 11. In this operation, force is applied to open the right and left insulation piercing blades 11 outwardly.
In general, an insulation piercing terminal is mass-produced, and a number of insulation piercing terminals are built in a connector housing in such a manner that they are adjacent to one another. Hence, there has been a strong demand for the provision of an insulation piercing terminal which is small in size, and light in weight. In order to decrease the weight of the insulation piercing terminal, it is essential to reduce the thickness of a metal plate which is formed into the insulation piercing terminal. And in order to miniaturize the insulation piercing terminal, it is necessary to decrease the width and the length of the insulation piercing terminal. For instance, in order to decrease the width of the insulation piercing terminal, it is essential to decrease the width of the insulation piercing blades forming the insulation piercing slot.
However, if the thickness of the metal plate, which is used to form the insulation piercing terminal, is decreased, or if the width of the insulation piercing blades is decreased, then the mechanical strength of the insulation piercing blades is decreased, as a result of which, when the wire is pushed in the insulation piercing slot, the right and left insulation piercing blades are opened outwardly.
In view of the foregoing, in the conventional insulation piercing terminal 1 shown in FIGS. 3 (a) to 3(c), the insulation piercing blades 11 are formed by bending inwardly the front and rear edge portions of the side walls 9 of the insulation piercing conductive section 4. However, the force which acts on the insulation piercing blades 11 when the wire is pushed in the insulation piercing slots, acts collectively on the junctions (the bent portions) of the side walls 9 and the bottom wall 7 (the junctions being decreased in thickness in the above-described bending operation; i.e., reduced in mechanical strength). As a result, the side walls 9 are apt to be bent outwardly, and accordingly, the insulation piercing blades 11 may be bent outwardly (opened). In order to overcome this difficulty, the recesses 18 are formed on the junctions of the side walls 9 and the bottom wall 7; however, the recesses 18 are not so effective in preventing the upper end portions of the side walls 9 from falling aside; that is, they are not so effective in preventing the insulation piercing blades 11 from being opened.